Fundamental steps of processing color light-sensitive materials generally include a color-developing step and a silver-removing step. That is, an exposed silver halide color photographic light-sensitive material is introduced into a color-developing step, wherein silver halide is reduced with a color-developing agent to produce silver and the oxidized color developing agent in turn reacts with a color former to give a dye image. Subsequently, the color photographic material is introduced into a silver-removing step, wherein silver having been produced in the preceding step is oxidized with an oxidizing agent (usually called a bleaching agent), and dissolved away with a silver ion-complexing agent usually called a fixing agent. Therefore, only a dye image is formed in the thus processed photographic material. In addition to the above-described two fundamental steps of color development and silver removal, actual development processing involves auxiliary steps for maintaining the photographic and physical quality of the resulting image or for improving the preservability of the image. For example, there are illustrated a hardening bath for preventing a light-sensitive layer from being excessively softened during photographic processing, a stopping bath for effectively stopping a developing reaction, an image-stabilizing bath for stabilizing the image, and a membrane-removing bath for removing the backing layer of the support.
The above-described silver removal may be conducted in two ways: one way uses two steps employing a bleaching bath and a fixing bath; and the other way is more simple and conducted in one step employing a bleach-fixing (or blixing) bath containing both a bleaching agent and a fixing agent for the purpose of accelerating the processing and eliminating work.
Red prussiate and ferric chloride, which have heretofore been used as bleaching agents, are good bleaching agents due to their large oxidizing power. However, a bleaching solution or bleach-fixing solution containing red prussiate can release poisonous cyanide by photolysis causing environmental pollution. Accordingly, the waste processing solution thereof must be made completely harmless in view of environmental pollution. A bleaching solution containing ferric chloride as a bleaching solution is not desirable because materials constituting vessels in which the solution is retained are liable to be corroded due to the extremely low pH and large oxidizing power of the solution. In addition, iron hydroxide is precipitated in an emulsion layer during the water-washing step provided after the bleaching step, resulting in stain formation.
On the other hand, potassium dichromate, quinones, copper salts, etc., which have been used as bleaching agents have weak oxidizing power and are difficult to handle.
In recent years, bleach processing using a ferric ion complex salt (e.g., aminopolycarboxylic acid-ferric ion complex salt, particularly iron (III) ethylenediaminetetraacetate complex salt) as a major component has mainly been employed in processing color photographic light-sensitive materials in view of acceleration and simplification of the bleaching step and the need to prevent environmental pollution.
However, ferric ion complex salts have a comparatively small oxidizing power and, therefore, have insufficient bleaching power. A bleaching or bleach-fixing solution containing the complex salt as a bleaching agent can attain some desirable objects when bleaching or bleach-fixing a low-speed silver halide color photographic light-sensitive material containing, for example, a silver chlorobromide emulsion as a major component. However, such a solution fails to fully remove silver due to insufficient bleaching power or requires a long time to bleach when processing a high-speed, color-sensitized silver halide color photographic light-sensitive material containing a silver chlorobromoiodide emulsion or silver bromoiodide emulsion as a major component, particularly color reversal light-sensitive materials comprising an emulsion containing larger amount of silver for photographic use or color negative light-sensitive materials for photographic use.
Other known bleaching agents than ferric ion complex salts include persulfates. Persulfates are usually used in a bleaching solution together with a chloride. However, this persulfate-containing bleaching solution has less bleaching power than ferric ion complex salts, thus requiring a substantially long period of time for bleaching.
As described above, bleaching agents which do not cause environmental pollution or corrode vessels and apparatuses have only a weak bleaching power. Hence, there has been a need to enhance the bleaching power of a bleaching or bleach-fixing solution containing a bleaching agent with a weak bleaching power, particularly a ferric ion complex salt or a persulfate.
In order to raise the bleaching power of a bleaching or bleach-fixing solution containing a ferric ion complex salt such as iron (III) ethylenediaminetetraacetate as a bleaching agent, it has been proposed to add various bleach accelerating agents to the processing bath.
Examples of such bleach accelerating agents include thiourea derivatives as described in Japanese Patent Publication No. 8506/70, U.S. Pat. No. 3,706,561, etc., selenourea derivatives as described in Japanese Patent Application (OPI) No. 280/71 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"), five-membered mercapto compounds as described in British Pat. No. 1,138,842, and thiourea derivatives, thiazole derivatives, and thiadiazole derivatives as described in Swiss Patent No. 336,257. However, these bleach-accelerating agents do not show a satisfactory bleach-accelerating effect, or they lack stability in the processing solution. Thus, they provide a processing solution having only a short effective life or which cannot be stored for a long time.